[PATCH] Enable info/refs gzip decompression in HTTP client

["Shawn O. Pearce" <spearce@spearce.org>]

From: "Shawn O. Pearce" <spearce@spearce.org>

Some HTTP servers try to use gzip compression on the /info/refs
request to save transfer bandwidth. Repositories with many tags
may find the /info/refs request can be gzipped to be 50% of the
original size due to the few but often repeated bytes used (hex
SHA-1 and commonly digits in tag names).

For most HTTP requests enable "Accept-Encoding: gzip" ensuring
the /info/refs payload can use this encoding format.

Disable the Accept-Encoding header on probe RPCs as response bodies
are supposed to be exactly 4 bytes long, "0000". The HTTP headers
requesting and indicating compression use more space than the data
transferred in the body.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 http.c                | 1 +
 remote-curl.c         | 4 ++--
 t/t5551-http-fetch.sh | 3 ++-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/http.c b/http.c
index 9bac1d8..345c171 100644
--- a/http.c
+++ b/http.c
@@ -818,6 +818,7 @@ static int http_request(const char *url, void *result, int target, int options)
 
 	curl_easy_setopt(slot->curl, CURLOPT_URL, url);
 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, headers);
+	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "gzip");
 
 	if (start_active_slot(slot)) {
 		run_active_slot(slot);
diff --git a/remote-curl.c b/remote-curl.c
index 3ec474f..4a0927e 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -393,7 +393,7 @@ static int probe_rpc(struct rpc_state *rpc)
 	curl_easy_setopt(slot->curl, CURLOPT_NOBODY, 0);
 	curl_easy_setopt(slot->curl, CURLOPT_POST, 1);
 	curl_easy_setopt(slot->curl, CURLOPT_URL, rpc->service_url);
-	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "");
+	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, NULL);
 	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDS, "0000");
 	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDSIZE, 4);
 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, headers);
@@ -449,7 +449,7 @@ static int post_rpc(struct rpc_state *rpc)
 	curl_easy_setopt(slot->curl, CURLOPT_NOBODY, 0);
 	curl_easy_setopt(slot->curl, CURLOPT_POST, 1);
 	curl_easy_setopt(slot->curl, CURLOPT_URL, rpc->service_url);
-	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "");
+	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "gzip");
 
 	headers = curl_slist_append(headers, rpc->hdr_content_type);
 	headers = curl_slist_append(headers, rpc->hdr_accept);
diff --git a/t/t5551-http-fetch.sh b/t/t5551-http-fetch.sh
index 2db5c35..380c175 100755
--- a/t/t5551-http-fetch.sh
+++ b/t/t5551-http-fetch.sh
@@ -32,13 +32,14 @@ setup_askpass_helper
 cat >exp <<EOF
 > GET /smart/repo.git/info/refs?service=git-upload-pack HTTP/1.1
 > Accept: */*
+> Accept-Encoding: gzip
 > Pragma: no-cache
 < HTTP/1.1 200 OK
 < Pragma: no-cache
 < Cache-Control: no-cache, max-age=0, must-revalidate
 < Content-Type: application/x-git-upload-pack-advertisement
 > POST /smart/repo.git/git-upload-pack HTTP/1.1
-> Accept-Encoding: deflate, gzip
+> Accept-Encoding: gzip
 > Content-Type: application/x-git-upload-pack-request
 > Accept: application/x-git-upload-pack-result
 > Content-Length: xxx
-- 
1.7.12.1.510.g5dd77d8